1. Field of the Invention
The present invention relates, in general, chemical sensing and, more particularly, to improved chemical sensors providing both selectivity and high sensitivity. Most particularly, the present invention relates to polysole
2. Description of Related Art
Detecting hazardous chemicals in our environment is fundamental to economic development, national security and the quality of life. The ever-increasing demand for better sensing or detection technologies to address needs in many different areas, including but not limited to, such as the detection of concealed explosives in airports, land and water mines, chemical agents that are extremely hazardous at trace levels, or industrial toxic waste produced by chemical plants. To be effective, a chemical sensing technology must provide a high degree of sensitivity, selectivity, stability, robustness and portability. Significant advances in the current chemical sensing technology will be immeasurably beneficial to national and global needs.
Of the many transduction mechanisms existing for chemical sensing, optical absorption, in particular, is widely used. Although the ultimate sensitivity of an optical absorption measurement is limited by quantum noise arising from the discrete nature of light, this limit is rarely achieved in practice.
Chemical sensors for nitroaromatics (NcQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. Rev. 2000, 100, 2537-2574; Albert, K. J.; Lewis, N. S.; Schauer, C. L.; Sotzing, G. A.; Stitzel, S. E.; Vaid, T. P.; Walt, D. R. Chem. Rev. 2000, 100, 2595-2626), which offer new approaches to the rapid detection of ultra-trace analytes from explosives, have attracted a great deal of attention in recent years, because explosives are important chemical species to detect in mine fields (Rouhi, A. M. Chem. Eng. News 1997, 75, 14-22) military applications, remediation sites, and homeland security applications (Fainberg, A. Science 1992, 255, 1531-1537). It is also important in forensic investigations, such as post-blast residue determinations (Barshick, S. A. J. Forensic Sci. 1998, 43, 284-293; Smith, K. D.; McCord, B. R.; McCrehan, W. A.; Mount, K; Rowe, W. F. J. Forensic Sci 1999, 44, 789-794). Metal detectors, widely used as portable instrumentation for field explosive detection, cannot locate the plastic casing of modern land mines. Trained dogs are expensive, difficult to maintain and are easily tired (Czarnik, A. W. Nature 1998, 394, 417-418). Physical detection methods for explosives include gas chromatography coupled with a mass spectrometer (Hakansson, K; Coorey, R. V.; Zubarev, R. A.; Talrose, V. L.; Hakansson, P. J. Mass Spectrom 2000, 35, 337-346), surface-enhanced Raman spectroscopy (Sylvia, J. M.; Janni, J. A.; Klein, J. D.; Spencer, K. M. Anal. Chem. 2000, 72, 5834-5840), nuclear quadrupole resonance (Anferov, V. P.; Mozjoukhine, G. V.; Fisher, R. Rev. Sci. Instrum. 2000, 71, 1656-1659), energy-dispersive X-ray diffraction (Luggar, R. D.; Farquharson, M. J.; Horrocks, J. A.; Lacey, R. J. J. X-ray Spectrom. 1998, 27, 87-94), neutron activation analysis, electron capture detection (Rouhi, A. M . Chem. Eng. News 1997, 75, 14-22), and cyclic voltammetry (Krausa, M.; Schorb, K. J. Electroanal. Chem. 1999, 461, 10-13). These techniques are highly selective, but some are expensive and others not easily fielded in a small, low-power package.
Most detection methods for explosives are only applicable to air samples due to interference problems encountered in complex aqueous media. Sensing TNT and picric acid in groundwater or seawater is important for the detection of buried unexploded ordnance and for locating underwater mines (Shriver-Lake, L. C.; Donner, B. L.; Ligler, F. S. Environ. Sci. Technol. 1997, 31, 837-841; Lu, J.; Zhang, Z. Analytica Chimica Acta 1996, 318, 175-179). There are also environmental applications for characterizing soil and groundwater contaminated with toxic TNT at military bases and munitions production and distribution facilities (Approaches for the remediation of federal facility sites contaminated with explosive or radioactive wastes.; U. S. Environmental Protection Agency: Washington, D.C., 1993). Organic polymers and optical fibers (Albert, K. J.; Myrick, M. L.; Brown, S. B.; James, D. L.; Milanovich, F. P.; Walt, D. R. Environ. Sci. Technol. 2001, 35, 3193-3200) have been previously studied to detect vapors of explosive analytes (McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. Rev. 2000, 100, 2537-2574; Albert, K. J.; Lewis, N. S.; Schauer, C. L; Sotzing, G. A; Stitzel, S. E.; Vaid, T. P.; Walt, D. R. Chem. Rev. 2000, 100, 2595-2626). The transduction methods used include absorption, fluorescence, conductivity, etc. Such simple techniques are promising because they can be incorporated into inexpensive and portable microelectronic devices. For example, a chemically selective silicone polymer layer on a SAW (surface acoustic wave) device has been shown to provide efficient detection for the nitroaromatic compounds (McGill, R. A.; Mlsna, T. E.; Mowery, R. In IEEE International Frequency Control Symposium, 1998, pp 630-633). Recently, it was reported that the fluorescence of pentiptycene polymers (Yang, J. S.; Swager, T. M. J. Am. Chem. Soc. 1998, 120, 5321-5322:; Yang, J. S.; Swager, T. M. J. Am. Chem. Soc. 1998, 120, 11864-11873) and polyacetylene (Liu, Y.; Mills, R. C.; Boncella, J. M.; Schanze, K. S. Langmuir 2001, 17, 7452-7455) are highly sensitive to nitroaromatic molecules. Previously Inventors communicated that the inorganic polymer, poly (tetraphenyl) silole 1, is an excellent material for the detection of explosives by fluorescence (Sohn, H.; Calhoun, R. M.; Sailor, M. J.; Trogler, W. C. Angew. Chem. Int. Ed. Engl. 2001, 40, 2104-2105). The work disclosed herein describes a broad class of easily prepared luminescent inorganic polymeric sensors for nitroaromatic compounds. Detection is based on photoluminescence quenching of polymers containing a metallole ring and Si—Si, Si—Ge, and Ge—Ge backbones.
Especially at this juncture of world history, there is a compelling need for highly sensitive and highly selective explosives detectors. There are approximately 5 mil in Europe, 7.5 mil US and 1 mil in Asia who had their baggage checked in the year 2000. Over $2 billion being spent to currently equip 76 largest US airports with X-ray CAT explosive detection systems. The United States Coast Guard oversees 6 million imported containers. US Customs initiated CSI (container security initiative ) after September 11th. It screens 489 million passengers/yr, comprised of 67 million air, 11 million ships, 328 million automobiles and 47 million pedestrians at 301 ports of entry.
US Military and NATO combined deploy more than 30,000 metal detectors as landmine sensors. There are about 100 million landmines, 6 million in Bosnia alone, scattered around world resulting in about 2000 casualties/month.
The US Homeland Security program must deal with protection of, but not limited to, water and air resources, food supplies, nuclear plants, chemical companies, oil refineries, gas storage areas, prisons, embassies, federal buildings, courts, corporate headquarters, banks, tunnels, Olympic venues, railway and subway terminals, underground parking areas, police stations, post offices, mailboxes, schools, lockers and passport scanners. Our waterways must be swept clean of water mines.
Furthermore, basic environmental monitoring is necessary, for example, of ground water at munitions facilities and ranges.
These efforts require astronomic expenditures of taxpayer money. For example, leading companies producing explosives detectors are:
Invision (CAT-ray Scan, unit cost 600K-1.5 mil, 268 units sold in 2001)
Barringer (ion scan, 45-60K),
Graseby Security (ion scan, 45K)
Thermedics (gc/chemiluminescence, 30-170K)
Quantum Magnetics (NQR, 65K)
AS&E (X-ray backscatter, 150K)
Explosive Detection Dogs (dogs, 8.5-25 K)
Moreover, ubiquitous metal detectors such as walk through (4-5K) and wands ($200-400). Dept. of Education advocates purchase 400,000 hand-held units.
In view of the above, it is clear that there is a great need for inexpensive and highly efficient inorganic polymer sensors that can detect nitroaromatic compounds, such as picric acid, nitrobenzene, 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) in air or seawater. An important aspect of the inorganic polymer sensors is their insensitivity to common environmental interferents.